Well I got to test ride both the 2010 Zero S and DS in the huge parking lot of Invesco Field at Mile High. My overall impression...wow! My only comparison is to my 2007 Vectrix (which is running great). Acceleration and overall punch are noticeably faster on the Zero bikes. Also the suspension is much more plush and would likely handle the occasional pothole or two much better than the Vectrix. The Zero bike are obviously way lighter too, only weighing about 288 lbs. Obviously the riding position is quite different than the Vectrix too. It is much more aggressive position leaning forward. Still comfortable but not nearly as comfortable as a scooter. The only differences between the S and the DS is the ride height is an inch higher on the DS and the tires are for street and dirt on the DS (and only street for the S). The bikes come with two seat options as well. I am taller at 6'4" so the regular seat was perfect for me, but nearly all of the people test riding were using the bikes with the low seat. This seams to be the same problem with the Vectrix and the later low seat option for shorter people. Obviously the big difference in sitting on the bikes with only your toes touching is the weight difference.
Overall, I was very impressed and am seriously thinking about getting one. But getting rid of my Vectrix...I don't think so. The Vectrix is too comfortable for leisure rides or the occasional ride with my wife on the back. Also there is obviously much more wind protection behind the Vectrix front end...riding the Zero in the winter would be out of the question unless you were very bundled up. That being said, I think I would go for the DS rather than the S because they are the same price and both are completely street legal, but the DS gives you the option for the occasional dirt or gravel road that comes in your path! Also, the real reason why the Zero is so enticing in Colorado, is that the final cost after the government and state rebate brings the cost down to only $4180!!! I think Oklahoma is even a bit better for the rebates but the CO EV rebate is amazing!